[ovn] tempest.scenario.test_network_v6.TestGettingAddress tests failing 100% times

In job neutron-ovn-tempest-slow tests from module tempest.scenario.test_network_v6.TestGettingAddress are failin 100% of times.

Example of failure:

https://storage.gra.cloud.ovh.net/v1/AUTH_dcaab5e32b234d56b626f72581e3644c/zuul_opendev_logs_2c7/707248/2/check/neutron-ovn-tempest-slow/2c77f9b/testr_results.html

Failure details:

Traceback (most recent call last):
  File "/opt/stack/tempest/tempest/common/utils/__init__.py", line 89, in wrapper
    return f(*func_args, **func_kwargs)
  File "/opt/stack/tempest/tempest/scenario/test_network_v6.py", line 244, in test_slaac_from_os
    self._prepare_and_test(address6_mode='slaac')
  File "/opt/stack/tempest/tempest/scenario/test_network_v6.py", line 225, in _prepare_and_test
    (ip, srv['id'], ssh.exec_command("ip address")))
  File "/opt/stack/tempest/.tox/tempest/lib/python3.6/site-packages/unittest2/case.py", line 690, in fail
    raise self.failureException(msg)
AssertionError: Address 2001:db8::f816:3eff:fe88:ea22 not configured for instance 55c9f9f2-3a99-4c0a-8536-be3cfe180381, ip address output is
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1392 qdisc pfifo_fast qlen 1000
    link/ether fa:16:3e:88:ea:22 brd ff:ff:ff:ff:ff:ff
    inet 10.1.0.9/28 brd 10.1.0.15 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fe88:ea22/64 scope link
       valid_lft forever preferred_lft forever